It is well known in the mining and shoring arts to utilize rock bolts to secure a wire mesh over the rock face of a mine roof or wall so as to stabilize the rock face and reduce the risk of injury to mine personnel by way of falling rock. Similar mesh screening means are sometimes used in excavation and shoring operations where rock or shale faces may be exposed. In both types of such operations, a suitably sized hole is drilled into the rock or shale material generally perpendicular to its face, and the rock bolt is inserted into the hole to a depth at which its threaded free end protrudes beyond the rock face by several inches. The rock bolts are retained in the drilled holes by any conventional means, and such retention means, together with the rock bolts themselves are well-known and are not part of the present invention.
After insertion of each rock bolt into a pre-drilled hole, a retention plate having a centrally positioned hole is typically placed over the protruding free end portion of the rock bolt and a conventional washer and nut are threaded onto this free end to hold fast the retention plate against the rock face and thereby stabilize the rock bolt within the rock material. Once the rock bolts are installed in this manner, a wire mesh can be applied over the rock face and held thereagainst typically by use of a gripper plate attached to each of the rock bolts.
Prior art gripper plates for this purpose are known, such as those disclosed in U.S. Pat. No. 5,207,535 (Saab) and U.S. Pat. No. 4,740,111 (Gagnon). During installation of prior art gripper plates, the gripper plate is pushed onto the rock bolt to secure the mesh screening, and is held in frictional engagement with the protruding end of the rock bolt by teeth, or other gripping means positioned on the body of the gripper plate. A socket wrench, or other device having a hollow cylindrical body portion is typically used as an installation tool to assist in driving home the gripper plate onto the protruding free end of the rock bolt in retaining engagement against the wire mesh. Frequently, the cylindrical installation tool is attached to a pneumatic drill, known as a "jackleg" to assist in such installation. Pneumatic drills are known to be quite heavy to lift, weighing perhaps seventy (70) pounds or more.
Mesh screening of the type under discussion is typically applied to support the ceilings and side wall faces of mine shafts, and the installer of the mesh has to work at levels at or above chest height, and frequently above his/her head. Thus, the installation of prior art gripper plates, necessitating, as it does, the use of a pneumatic drill, results in the installer having to lift the weight of the pneumatic drill, the installation tool, and a gripper plate attached to the installation tool, in order to install each gripper plate. The process is awkward, time consuming and requires significant strength and endurance on the part of the installer. Moreover, conventional gripper plates require aligned placement of the installation tool within a plurality of upstanding tabs or the like formed integrally with the lower surface of the gripper plate. The alignment is done manually by the installer. Thus, installing a gripper plate involves the steps of: retrieving a gripper plate by hand from a stored supply of gripper plates; manually fitting the gripper plate on the free end of the installation tool within the alignment tabs of the gripper plate; manoeuvring the installation tool, (and the attached pneumatic drill), with the gripper plate balanced thereon in said aligned configuration, into position adjacent to the already installed rock bolt; and installing the gripper plate over the wire mesh on the protruding end of the rock bolt by activation of the pneumatic drill.
Placement of the gripper plate in aligned relation on the free end of the of the installation tool requires several seconds for each gripper plate installed, and does not prevent the gripper plate from tilting or falling off of the installation tool while being lifted to the mine ceiling for engagement with the rock bolt. Moreover, such vertical tilting frequently results in the gripper plate contacting the threaded end of the rock bolt at an angle which causes deformation of the gripper plate teeth and inadequate and unpredictable frictional engagement by the gripper plate teeth with the threads of the rock bolt during the turning or pressing of the gripper plate into position on the protruding end of the rock bolt. When this occurs, the amount of weight which a mis-aligned gripper can support before disengagement from the rock bolt decreases, with a consequential decrease in the safety margin of the installation. In order to ensure uniform safety standards in a mining environment, such an improperly installed gripper plate would have to be removed and replaced.
Additionally, while manoeuvring the installation tool/gripper plate combination towards the protruding free end of the rock bolt, it is not uncommon for the gripper plate aligned and balanced on said free end of the installation tool to fall to the mine floor, posing a safety hazard to the installer or other workers in the area. Moreover, the retrieval of fallen gripper plates is a source of delay and frustration in the process of installing the mesh screening if they are retrieved, and an additional cost to the mine operation if they are not.
Accordingly, it is an object of the present invention to provide a system for securement of a mesh screening means on the protruding, threaded end portion of a rock bolt inserted into a rock face having a gripper plate and an installation tool which are easily and reliably engageable with one another.
It is a further object of the present invention to provide such a system in which no fine manual alignment of the installation tool with respect to a gripper plate is required prior to the engagement thereof.
It is a further object of the present invention to provide such a system in which a gripper plate and installation tool are self aligning and remain secured in engagement one with the other until the teeth of the gripper plate have fully engaged the threaded end of the rock bolt.
It is yet another object of the present invention to provide such a system which will completely install a gripper plate using the installation tool alone, and does not necessarily require the use of a pneumatic drill or other subsidiary means to assist in installing the gripper plate on the threaded end of the rock bolt in fully secured relation.
It is still a further object of the present invention to provide such a system in which the installation tool is of lighter weight than the conventional combination of an installation tool used in combination with a pneumatic drill to increase the dexterity and reduce the fatigue of an installer.
It is still a further object of the present invention to provide such a system in which both the gripper plate and the installation tool are simple, robust, and cost effective to manufacture.
It is yet a further object of the present invention to provide a method for installing a gripper plate on the protruding, threaded end of a rock bolt inserted into a rock face utilizing the system of the present invention.